1. Technical Field
The present invention relates to an ultrasonic cleaning device by single-wafer spin cleaning, an immersion type ultrasonic cleaning device, and an ultrasonic cleaning device for cleaning a large substrate.
2. Description of the Related Art
<Single-Wafer Spin Cleaning>
FIG. 24 is a sectional view illustrating a prior art spot-shower type ultrasonic cleaning device for single-wafer spin cleaning. This ultrasonic cleaning device is the one for cleaning an object to be cleaned 101 having a flat plane such as a semiconductor wafer. This device has a mechanism (not shown) for spinning the object to be cleaned 101 in order to clean the entire surface of the object to be cleaned 101, an ultrasonic transducer 103 for providing ultrasonic energy to a cleaning liquid, a cleaning-liquid supply port 105 for supplying the cleaning liquid to the ultrasonic transducer 103, a nozzle 104 for injecting a cleaning liquid 102 provided with the ultrasonic energy to the object to be cleaned 101 in a spotted manner, and a swing mechanism (not shown) for swinging the nozzle 104 (See Patent Document 1, for example).
As mentioned above, with the ultrasonic cleaning device shown in FIG. 24, since an ultrasonic irradiation region is a point (spot), there has been required a swing mechanism for swinging the nozzle 104 in order to clean the entire surface on the object to be cleaned 101. Also, the larger a substrate to be cleaned is, the more time it takes for swinging it, and there is a problem that cleaning time of the device cannot be reduced.
Also, in order to reduce a distance between the nozzle 104 and the object to be cleaned 101, the nozzle 104 needs to be installed in the vicinity on the object to be cleaned 101, which makes workability poor. Also, since an installation space for the nozzle 104 is limited, it is difficult to install a plurality of nozzles.
For the cleaning liquid, in addition to deionized water and functional water in which gas (nitrogen, hydrogen, helium, ozone and the like) to improve a cleaning effect or gas (carbon dioxide) having an antistatic action are added to the deionized water, ammonia hydrogen peroxide solution with the purpose of removing particles, dilute hydrofluoric acid with an etching action, a stripper liquid for removing a resist film and the like are used. Since these cleaning liquids pass through the inside of the ultrasonic transducer 103, a member resistant against the cleaning liquid should be selected for the housing 106, an oscillation plate, the nozzle 104, and a packing, which are portions to contact the liquid. Also, in order to prevent contamination from the member, cleanliness of each member should be maintained.
FIG. 25 is a sectional view illustrating a prior-art probe (solid rod) type ultrasonic cleaning device for single-wafer spin cleaning. This ultrasonic cleaning device is a device for cleaning the object to be cleaned 101 having a flat plane such as a semiconductor wafer. This device has a mechanism (not shown) for spinning the object to be cleaned 101 in order to clean the entire surface of the object to be cleaned 101, a cleaning liquid supply nozzle 107 for supplying a cleaning liquid 102 to the surface of the object to be cleaned 101, a probe (solid rod) 108 to contact the cleaning liquid 102 supplied to the surface of the object to be cleaned 101, the ultrasonic transducer 103 for providing ultrasonic energy to the probe (solid rod) 108 through a heat transfer member 109, and a coolant supply port 110 and a coolant discharge port 111 for supplying and discharging a coolant for cooling the heat transfer member 109 (See Patent Document 2, for example).
In the above-mentioned ultrasonic cleaning device shown in FIG. 25, since the ultrasonic irradiation region is on a line along the probe (solid rod) 108, time required for cleaning the entire surface on the object to be cleaned 101 can be largely reduced as compared with the spot shower type cleaning device. Also, since a swing mechanism for swinging the probe (solid rod) 108 is not needed, a space required for installation of the probe (solid rod) 108 can be reduced.
Also, since a liquid contact portion is only the probe (solid rod) 108, it is only necessary to select a member resistant against the cleaning liquid 102 only for the probe (solid rod) 108. The probe (solid rod) 108 is made of an inactive non-contaminant such as quartz, and contamination from the liquid contact portion can be easily prevented.
Also, in order to oscillate the probe (solid rod) 108 formed from a solid material with a high density such as quartz, an acoustically large load is applied to an oscillating element and causes a large amount of heat. Thus, with such a probe (solid rod)-type ultrasonic cleaning device, energy is propagated to the probe (solid rod) 108 through the thermally conductive member 109 for cooling the ultrasonic transducer 103 and the probe (solid rod) 108. Then, in order to efficiently cool the heat transfer member 109, a coolant passing through the heat transfer member 109 needs to be circulated.
Also, if the probe (solid rod) 108 is oscillated by the drive of the ultrasonic transducer 103, standing wave distribution is generated in the probe (solid rod) 108 as shown in FIG. 26. A wavelength λ of the standing wave distribution can be calculated as λ=V/F from a sonic speed V and an operating frequency F in the probe (solid rod) 108. If the probe (solid rod) material is quartz, the sonic speed V=6000 m/s, and in the case of the operating frequency F=1 MHz, the wavelength λ=6 mm.
Since the sonic speed V and the operating frequency F in the probe (solid rod) 108 have a temperature characteristic, it is necessary to make temperatures of the probe (solid rod) 108 and the ultrasonic transducer 103 constant in order to maintain the standing wave distribution in the probe (solid rod) 108. Therefore, cooling temperature control by a coolant needs to be executed.
Also, in order to form the standing wave distribution, it is necessary to design the probe length with integral multiple of λ/2. Since the standing wave distribution is not formed if the probe (solid rod) length is varied even slightly, predetermined oscillation amplitude is not obtained if the ultrasonic transducer 103 is driven. Therefore, it is necessary to manufacture the probe (solid rod) 108 with an accurate probe length.
Also, the cleaning effect can be obtained at a position of antinodes of displacement amplitude shown in FIG. 26, but the cleaning effect lowers at a position of nodes. An interval between nodes is λ/2=3 mm, and the cleaning effect lowers with the interval of 3 mm.
Also, in the ultrasonic cleaning device shown in FIG. 25, the length of the probe (solid rod) 108 needs to be lengthened approximately to a radius of the object to be cleaned 101. Thus, in order to cope with an increase in diameter of the object to be cleaned 101, the length of the probe (solid rod) 108 needs to be lengthened accordingly. For example, for a 200-mm wafer, the length of the probe (solid rod) 108 needs to be approximately 100 mm, and for a 300-mm wafer, the length of the probe (solid rod) 108 needs to be approximately 150 mm. However, the probe length that can be driven is limited, and if the probe (solid rod) reaches certain length, it can no longer be driven due to an acoustic load applied to the ultrasonic transducer. Therefore, it is difficult to cope with an increase in diameter larger than the 300-mm wafer with the ultrasonic cleaning device in FIG. 25.    Patent Document 1: Japanese Patent Laid-Open No. 2007-289807 (FIG. 1)    Patent Document 2: Japanese Patent No. 3493492 (FIG. 1)<Immersion Type Cleaning>
FIG. 27(A) is a sectional view of a prior-art immersion type ultrasonic cleaning device, and FIG. 27(B) is a sectional view obtained by cutting the ultrasonic cleaning device in a direction perpendicular to the section shown in FIG. 27(A).
This ultrasonic cleaning device has a general cleaning tank used in the immersion type cleaning of a semiconductor wafer and this cleaning tank has an indirect cleaning structure in which an inner tank 112 filled with a cleaning liquid is placed on an outer tank (not shown) in which an ultrasonic transducer 113 is installed on a bottom face. The cleaning liquid is introduced into a jet pipe 114 from a cleaning liquid inlet 114a, and the introduced cleaning liquid is discharged from a side surface of the jet pipe 114 into the inner tank 112 as shown by an arrow and is overflowed from the upper part of the inner tank 112.
A wafer as an object to be cleaned 115 installed in the inner tank 112 is supported by a carrier (transporting unit) 116 for transporting wafer. Ultrasonic energy is irradiated from the bottom face, but the ultrasonic energy hits a receiver portion 116a in bottom part of the carrier 116, and there is a problem that a shaded portion in which ultrasonic energy does not reach the wafer is caused or air bubbles which adversely affect cleaning efficiency are generated.
Also, since the ultrasonic transducer 113 is installed on the bottom face of the cleaning tank, there is a need to provide a cleaning liquid drain port 112a on the side surface of the inner tank 112. If the cleaning liquid drain port 112a is provided on the side surface, there is a problem that drainage of the cleaning liquid takes time or the cleaning liquid cannot fully be drained from the inner tank 112.
<Large Substrate Cleaning>
A substrate size of FPD or a solar cell is getting larger, and a substrate size can reach even 2.8 m×3.5 m. In the case of a substrate with a size up to 1 m×1 m, the substrate is disposed horizontally, and the cleaning liquid provided together with ultrasonic energy is ejected like line shape shower onto this substrate by so called Ultrasonic Line Shower Cleaning Unit. In this way, the substrate is cleaned by the cleaning liquid.
However, as the substrate size gets larger, considering the above cleaning method for a 1.5 m×1.5 m substrate, for example, the cleaning liquid to be supplied to the substrate needs a large flow rate exceeding 100 L/min, the weight of the transducer reaches 18 kg, and as a result, manufacture and installation of the cleaning device becomes extremely difficult. Therefore, there is a problem that the cleaning device with the above cleaning method cannot process the substrate size exceeding 1 m×1 m.
Also, if the substrate with a size of 1.5 m×1.5 m or more is placed horizontally, the substrate is deflected by the weight of the discharged cleaning liquid, and it is foreseen that the liquid cannot be completely drained or dried.